Petrophysical Properties of Oomoldic Limestones in the Lansing-ÐKansas City Groups, Kansas: Tools for More Accurate Evaluation and Enhancing Recovery

Alan P. Byrnes, John Doveton, W. Lynn Watney, Saibal Bhattacharya. Kansas Geological Survey, 1930 Constant Avenue, The University of Kansas, Lawrence, KS 66047,   [email protected]

Cyclic oomoldic limestones of the Pennsylvanian Lansing-ÐKansas City have produced over 1 BBO in Kansas and represent important improved/enhanced oil oil-recovery (IOR/EOR) targets. Properties within meter-scale parasequences that comprise the limestone reservoirs result from interaction of depositional architecture and particle texture with subsequent near-surface and deep diagenesis leading to oomoldic porosity, and sometimes fracturing. Frequently- observed micritized ooids and micritic calcite cements associated with terminal subaerial exposure at the top of the depositional sequence is are associated with poorer reservoir quality. Underlying enhancement of permeability by improved oomoldic connectivity is common. A general decrease in permeability with depth, often associated with little decrease in porosity, frequently characterizes the lower portion of the oomoldic interval.

Because pay intervals,  that often exhibit low gamma ray,  also are often thin (66% < 6 ft [2 m] thick, 2 m;, 45% < 4 ft,  [1.3 m]) and exhibit high porosity (8-Ð30%), a single set of petrophysical properties is often assigned to the entire interval although petrophysical properties can vary significantly foot-by-foot. The relation between permeability (k=0.001-Ð400md) and porosity (f=5-35%) is significantly influenced by the connectivity of the oomoldic pores, and Archie cementation exponents (2<m<5) are a function of k and f: m Å (-0.024 logk + 0.12)f + 1, resulting in correct log-calculated water saturations varying by up to 80% from values calculated using m = 2.. Laboratory-measurements of residual oil saturation to waterflood indicate this depends on mold connectivity, initial oil saturation, and height above the free water level. Simulations using foot-specific m and end-point saturations reveal that typical well performance is often consistent with 1-Ð3 feet of high high-quality reservoir. Thus detailed application of petrophysical properties are necessary for improved initial reservoir assessment, production management, and IOR/EOR evaluation and implementation.